Computer control system for rolling metal strips using feed-forward and prediction

ABSTRACT

A rolling method wherein the material size may be altered during a normal rolling operation by prediction and feed-forward control comprising predetermining a basic pattern for altering roll peripheral speed corresponding to a fixed pattern of roll opening (or strip gauge), computing the actual amount of alteration of the above speed based on at least a command for gauge alteration and feeding forward the computed value corresponding to roll peripheral speed alteration to each stand.

United States Patent Tohru Arimura Kawasaki-shl;

Masamoto Kamata, Kawasaki-sill; Morio Salto, Kawasaki-shi; Terumi Okamoto, Fukuyama-shi, all of, Japan [72] Inventors [2]] App]. No. 822,433

[22] Filed May 7, 1969 [45] Patented Sept. 7, 1971 [73] Assignee Nippon Kokan Kabushiki Kaisha [32] Priority May 9, 1968 [33] Japan [54] COMPUTER CONTROL SYSTEM FOR ROLLING METAL STRIPS USING FEED-FORWARD AND PREDICTION 7 Claims, 13 Drawing Figs.

[52] U.S. Cl 72/8, 72/11 [51] lnt.Cl ..B2lb37/l2 [50] Field of Search 1.

[56] References Cited UNITED STATES PATENTS 3,036,480 5/1962 Schwab 72/1 1 X 3,169,421 2/1965 Bloodworthm 72/1 1 3,174,317 3/1965 Camp 72/12 3,186,201 6/1965 Ludbrook et a1 72/9 3,212,310 10/1965 Brys 72/12 3,332,263 7/1967 Beadle et a1 72/7 3,457,747 7/1969 Yeomans... 72/19 3,508,425 4/1970 Cox 72/9 Primary Examiner-Milton S. Mehr AlrorneyFlynn & Frishauf ABSTRACT: A rolling method wherein the material size may be altered during a normal rolling operation by prediction and feed-forward control comprising predctermining a basic pat tern for altering roll peripheral speed corresponding to a fixed pattern of roll opening (or strip gauge), computing the actual amount of alteration of the above speed based on at least a command for gauge alteration and feeding forward the com puted value corresponding to roll peripheral speed alteration to each stand.

PATENTEU SEP 7 |97l SHEET [11 OF 11 I 6 mm on 91 aw v 35 m 9 2 mm mm 3 5 mm on #2 -65 ALTERING RATE OF ROLL PERIPHERAL SPEED PATENIEUSEP 719m 3.603.124

SHEU U5UF11 FIG. 7 Ah5=OJmm 61 d2 63 6.4 6.5 d6 of? 0 8 0 9 lb sec Lb I [5 I A PATENTEU SEP 7 WI sum 0? HF 1 mQI PATENTED SEP 7 ISTI sum 09 0F 11 PATENTED SEP 7 I97! SHEET 10 CF 11 PATENTED SEP 7 12m SHEET 11 HF 11 COMPUTER CONTROL SYSTEM FOR ROLLING METAL STRIPS USING FEED-FORWARD AND PREDICTION This invention relates to a control system for rolling metal and more particularly for rolling thin metal strips wherein altering the thickness of the strip during the rolling operation is achieved freely and safely.

In large-scale works, it is well known that a lowering of cost is obtained with mass production by using a continuous hotand cold-rolling process for making metal strips having the required thickness. That is, a single strip having the same size over the overall length is made from slab by a continuous hotrolling mill, two or three coils of such strips are welded into one strip, and then this welded strip is passed through a coldreducing tandem mill. The above-mentioned process has been employed as the best suited process for mass production. However, there are many instances where it is necessary to produce small orders for different sizes. In such a case slabs having different unit weights must be used. This resulted not only in lowering the productivity of modern continuous rolling mills, but also in considerable operational difficulties.

An object of the present invention is to provide a control system where it is possible to freely and stably alter the strip size, particularly the thickness, without adversely affecting the production line.

Another object of the present invention is to provide a control system where it is possible to produce a continuous rolling coil having a precise thickness, even when the pass schedule is altered at will during the rolling operation.

A further object of this invention is to provide a control system where it is possible to completely utilize the prior AGC system.

A still further object of this invention is to provide a control system where it is possible to use the largest slabs or coils at all times if it is within the capacity of the employed mill without giving any consideration to said size changes.

The principles and characteristics of this invention, as well as other objects and advantages will be more clearly seen from the following descriptions taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a block diagram of a prior art control system in an ordinary tandem cold-reducing mill;

FIG. 2 shows diagrams illustrating the variation with outgoing thickness and forward tension of each stand in FIG. 1 under uncontrolled conditions;

FIG. 3 shows the control pattern of rolling speed at the first stand;

FIG. 4 shows the control pattern of rolling speed at the second stand;

FIG. 5 shows the control pattern of rolling speed at the third stand;

FIG. 6 shows the control pattern of rolling speed at the fourth stand;

F IG. 7 shows the control pattern of rolling speed at the fifth stand;

FIG. 8 shows the control pattern of rolling speed at all stands;

FIG. 9 shows a block diagram of a program control system according to this invention;

FIG. I is a block diagram of an embodiment of the present invention using an interstand tension meter;

FIG. 11 is a block diagram of an embodiment of the present invention using an interstand thickness meter; and

FIG. 12 is a block diagram of an embodiment of the present invention using a mixed control system.

In automatic control systems commonly known in the art and as shown in FIG. I, the manner of operation is as follows:

A metal strip is uncoiled by uncoiler l and is rolled through the first rolling stand 2, the second stand 3, the third stand 4, the fourth stand and the fifth stand 6. It is then coiled on tension reel 7. In the constant rolling of the above tandem mill, it is well known that the relationship between roll opening and peripheral speed of said roll obeys the flow-constant law wherein the product of outgoing thickness of the strip the rolling speed is constant. Both the thickness and the speed at each stand are determined by the flow-constant law. For realizing this law, facilities are arranged on each stand: reduction devices l4, l5, l6, l7 and I8 accompanied by a set of Motor-Generator systems 21-22, 25-26, 28-29, 31-32 and 34-35, and speed regulators 20, 24, 27, 30 and 33 which are able to freely control the reduction speed. The speed regulators are driven with ordinary Ward-Leonard systems respectively. Secondly, the rolling speed is, of course, to be con trolled by means of regulating the rotational speed of the rolls. Concretely speaking, at each stand, the rolls are driven by the above-mentioned Ward-Leonard system and is controlled by means of speed regulators 56, 55, 54, 53 and S1 accompanied by a set of Motor-Generator systems 37-38, 40-41, 43-44, 46-47 and 49-50 respectively. The rotational speeds of the motors 37, 40, 43, 46 and 49 are respectively detected by rotation meters 36, 39, 42, 45 and 48, and the appropriate feedback signal is sent to the above speed regulators.

It is, however, customary to accompany the abovementioned control facilities with some automatic gauge control (AGC) system in order that a precise finishing thickness of the strip is maintained. This AGC system usually consists of two kinds of local feedback devices. One of said feedback devices is for the first stand, for making the roll opening change in accordance with the deviation Ahl of the outgoing strip thickness, which is detected by an X-ray thickness meter, from the predetermined thickness. A signal which is proportional to the rotational speed of motor 21, detected by rotation meter 23 and the other signal from the above thickness meter are fed back together into the screw down autocontrol device 19 so that the optimum reduction rate is easily obtained. While this is a rough control for obtaining the required thickness, a precise control is provided at the final stand, the fifth stand in FIG. 1. Both the signal, which is the deviation A from the predetermined thickness, detected by an X-ray thickness meter 9 and the other signal, which is a function of the rotational speed of the motor 49, are together fed back into the rolling speed regulator 51. In this case, the signal fed back is transmitted through the automatic tension regulator 52. While the Motor-Generator system 49-50 is so adjusted that the tension between No. 4 and No. 5 stands is changed and the above deviation Ah 5 becomes zero, sufficient accuracy of finished thickness is easily obtained.

The above AGC system is required for hotand cold-rolling mills. It is, however, well known that further additional devices are required in order to stabilize the AGC system and to maintain the whole rolling function normal. Tension meters 10, ll, 12 and I3 shown in FIG. 1 indicate the interstand tension and the tension is kept to a suitable value in accordance with the rolling resistance and force of the strip. If the tension value is too high, the strip will be broken. 0n the other hand, if the tension is too low, the strip may be folded due to looping of the strip. Consequently, it is possible that a roll will be broken by instantaneously striking the folded strip. Even if the strip passes through the rolling mill, it is impossible to produce a strip having the required thickness. The feature of the prior control system mentioned above, even when including other modified systems such as that shown in U. S. Pat. No. 3,332,263, is to improve the accuracy of strip thickness only by a feedback system. It will be obvious that such a control system should have some limitations by the reason that devia' tions detected in a constant pass schedule for the same size materials are only adjusted by the feedback system. That is, it is not possible to practically change material sizes during a rolling operation. According to our experiments, it has been confirmed that the most effective method of solving the above-mentioned problems consists in keeping the interstand tension constant during rolling. For realizing the above theory, it is necessary that a feed-forward system be employed in place of a feedback system as described above. That is, the altering pattern of the roll peripheral speed for each of stands must be measured and utilized for control. Each of stands, of course, has a different altering pattern in accordance with the mill facilities employed. Accordingly, when an altering order of strip size is computed on the basis of said altering pattern respectively, the size change is immediately dealt with and a fluctuation in the interstand tension is simultaneously compensated for. Then, the normal rolling operation is easily effected.

The most important feature of the present invention lies in the details of the dynamic manner in which the conditions of each mill stand actually employed are measured, and in the manner in which a suitable computer memory is used for alter ing the pattern of the roll peripheral speed. That is, the roll peripheral speed, which is altered in response to the adjustment of roll opening brought about by a gauge alteration in rolling, must be altered without fail. In accordance with the present invention, the interstand tension is kept constant and the rolling operation is stably carried out. Thus, for altering the roll peripheral speed, the equation below has been obtained as a result of many experiments:

Ais a symbol which denotes the deviation;

V is the roll peripheral speed;

i is the stand number;

is the Laplacean;

I1, is the outgoing thickness of the ith stand;

T, is the time (seconds) which strip is transferred from the ith stand to the i-Hth stand; and A,, B,, C, and D, are constants decided by the incoming thickness, outgoing thickness and tension, material properties, type of lubricant, rolling speed and construction of the rolling mill.

lt will be understood from the above equation that a predicting control for the roll peripheral speed must operate in response to alterations of the roll peripheral speed and the outgoing thickness in the next stand and the outgoing thickness in the present stand. The above predicting control is necessary for keeping the interstand tension constant during a transition stage from a present constant rolling condition to a next constant rolling condition. Further referring to equation I, it is obvious that the speed at the i+l th stand should also be adjusted with forecasting computations because the alteration of outgoing thickness in the ith stand reaches the i-l-lth stand after Tseconds. Only by these prediction means, is it possible to keep the interstand tension constant and for the rolling operation of the present invention to be brought to practice.

With a view to altering a product thickness, it was attempted to change the roll opening of each stand under uncontrolled conditions of the roll peripheral speed. Diagrams as shown in FIG. 2 were obtained as a result of the above test, where the variation with outgoing thickness and forward tension of each stand in FIG. I are illustrated. It is well understood from FIG. 2 that the interstand tension greatly changes and a stable rolling operation is hardly achieved. FIG. 2 shows that the alteration of the tension between No. 2 and No. 3 stands and between No. 4 and No. 5 stands is larger. concretely speaking, the preset value of interstand tension, which is [5.4 kg./mm. between No. 2 and N0, 3 stands and l4.l kgjmm. between No. 4 and No. 5 stands, fell to zero after 0.21 second and after 0.07 second respectively, as shown in FlG. 2. These facts show that it is impossible to stabilize the rolling operation with prior arLtechniques. In this case, if these matters are computed with the above equation 1, the controlled amount of each roll peripheral speed in response to altering the amount of roll opening according to an order of gauge alteration in said rolling will be easily obtained. These details, which have been actually calculated, are as follows:

An example of pass schedule in normal cold-reducing conditions [actual operation) Thickness of Hot Strip 3.2 mm. Radius of Work-Roll 273 mm Radius of Backup Roll 7 Ill mm.

TABLE I Reduction Schedule When strip thickness in table I is altered during rolling, the amount alteration of the roll opening accordant with the above gauge alteration is calculated as in table II, below. This is shown as the amount of alteration of roll opening in which the outgoing thickness of each stand is altered by a unit amount (0.1 mm).

TABLE II Amount of alteration of roll opening (mm.) No. I stand 022 No. 2 stand 0.23 No. 3 stand I 3| No. 4 stand 0 45 No. 5 stand I) As mentioned above, the amount of alteration of the roll opening should be computed on basis of the above equation.

Accordingly, the control pattern of each stand, which is concerned with said rolling speed, must have been predecided by said equation as the first step. FIG. 8 shows a typical control pattern employed in the above example. In the control pattern of FIG. 8, the abscissa represents the time (seconds) and the ordinate represents the rate of alteration of the roll peripheral speed when the outgoing thickness of each stand is altered by a unit amount (0.l mm. An amount of alteration of said roll peripheral speed at each stand corresponding to the amount of alteration of roll opening as shown in table II is adjusted based on the control pattern of FIG. 8. FIGS. 3, 4, 5, 6 and 7 show an actual alteration pattern of the roll peripheral speed concerned with the above Tables I and II. The abovementioned pattern provides completely predicted control, ie a feed-forward system, and it is possible to easily prevent the interstand tension from changing. It will be understood that an online computer is necessary in order to realize the above system. When a gauge alteration in rolling is required, first the command for altering the roll opening is issued from said computer, which is computed on the ground of the memorized control pattern. Another command for altering the roll peripheral speed is issued so that the interstand tension is stably and continuously kept constant. It is an important fea ture of this invention that such alteration commands are given to the next succeeding stand in order, before the strip reaches said next succeeding stand.

In order that the above-mentioned gauge alteration process should be put in practice, a program control system is recommended. This system is very effective for any rolling speed and a block diagram thereof is shown in FIG. 9 by way of example. The mechanism of FIG. 9 is made up ofa command device 76 concerned with gauge alteration, online computer 75 and signal converter 77, which is additionally provided with the facilities of FIG. 1. The computer 75, given a command of gauge alteration, first calculates a new pass schedule and determines the required altering amount of roll opening and of roll peripheral speed. After such calculated values are converted into analog values by converter 77, the former signal is transmitted to the roll-opening regulators 19, 24, 27, 30 and 33 and the latter signal to roll peripheral speed regulators 56, 55, 54, 53 and 51, respectively. Each of the above command signals is applied to an ordinary AGC system, e.g. as shown in FIG. I. The forecasting control as mentioned above can make the interstand tension always constant without a breakage of the strip or damage to the rolls. Such a feed-foreward control system was extremely effective for not only gauge altering in rolling, but also for use with welded coils having different thicknesses.

FIG. shows another example of the present invention. The mechanism of FIG. 10 is characterized by positive utilization of ordinary interstand tension meters 10, ll, 12 and I3 as shown in FIG. I. The response of the control system which utilizes such tension meters is inferior to that of the program control system of FIG. 9. The above system, if applied to cases where the rolling speed is comparatively slow, is able to exhibit sufficient effects. In this case, it is noted that a change of interstand tension does not occur independently. The change is subject to the roll peripheral speed in front and in the rear of said tension meters, outgoing thickness of strip and rear stand tension. Accordingly, the basic computation expression of the above process becomes a formula that is a variant of said equation I. Accordingly, we have derived from experiments the following applicable relation: AI4,,=A','Ah,+B,e-""Ah,+C,,,Ah, ,+D',- AV,+E',-Atf,+F',-,,

ftu Where:

Ah, is the reduction alteration amount in the ith stand;

AV, is the alteration amount of the roll peripheral in the ith stand;

Atf, is the alteration amount of the tension at that time,

A',, B',, C',,,, D,, E, and F',,, are constants determined by rolling conditions as mentioned in connection with equa tion I.

When strip thickness is altered during rolling, the alteration of interstand tension is easily eliminated by the following requirement in equation 2.

fr== Accordingly, a necessary amount of alteration of the roll peripheral speed is given by following equation:

AV ,=A,-Ah,+B',e i'Ah,+C',,,'Ah,+,+D','AV,+F',,,-Atfl,,

This equation 3 becomes the control pattern memorized within the online computer in place of that of equation I. When a command for gauge alteration is given to the system of FIG. 10, a change of Ah, is automatically determined. Accordingly, an altering value of the front stand tension meters 10, 11, I2 and I3 to the converter 77 and simultaneously a value of roll peripheral speed is transmitted from each rollrotating meter 36, 39, 42, 45 and 48 to the converter 77. This signal is converted into a digital value and is transmitted to the computer 75. Here, an altering amount of the roll peripheral is obtainedv After this, the required altering value is converted into an analog value and this value is fed-forwarded to the roll peripheral speed regulators 56, 55, 54, 53 and 52 respectively. Thus, alteration of the interstand tension is quickly compensated for and again, a normal reducing operation is stably carried out.

The gauge alteration in rolling may be detected by a thickness meter arranged at the delivery side of each stand. It is well known that an X-ray gauge may be employed as such a thickness meter. FIG. 11 is an example of the above process. when such a thickness meter is used, the gauge alteration con trol is possible to be brought to practice by the altering pattern of the roll peripheral speed in accordance with equation I. In this case, the outgoing strip thickness at each stand is directly measured by X-ray gauges 8, 57, 58. 59 and 9 and simultaneously the roll peripheral speed is measured by rotating meters 36, 39, 42, 45 and 48 respectively. The obtained values are transmitted to computer 75 through converter 77 and the required alterations are computed. The computed values are fed-forward to next stand in order. While such a control system has slower responsiveness than that of the above program control system, there is still sufiicient possibility of stable gauge alteration for rolling mills having a lower rolling speed.

FIG. 12 shows a control system wherein an ordinary rolling force meter is employed. The rolling force detected by each load-cell 60, 61, 62, 63 and 64 and an output signal of each roll-rotating meter 36, 39, 42, 45 and 48 is transmitted to the computer '75. In this process, as is well known from W. C. F. Hessenbergs works, that the relationship between the amount of alteration of strip thickness and that of rolling force is exhibited as follows:

Ah, is the amount of alteration of thickness;

AS, is the moving amount of the screwdown;

AP, is the amount of alteration of rolling force; and

AM is the mill spring value.

According to the above formula 4, the required amount of alteration of the outgoing thickness at each stand is possible to be easily computed. The control process based on formula 4 is the same as mentioned above. The features of this system (FIG. 12) lie in the possibility of detecting a change of outgoing thickness without any time lag, and with a lower cost. The utility of this system is higher than that of thickness meter system of FIG. 11.

The above-mentioned control system, i.e. program, tension meter, thickness meter and rolling force meter, are basic control processes. These systems, of course, can be independently employed. It is, however, true that there is some limit in their application. That is, according to many experiments, the system of FIG. 12 was unable to deal with an alteration of the interstand tension based on other causes except with the command of the gauge alteration by the computer in rolling. It is, on the other hand, confirmed that each system of FIGS. 10, II and 12 has an ability of dealing with the above alteration. By contrast, the responsiveness of these systems is inferior to that of the system of FIG. 9. Accordingly, combinations of suitable systems from the above-mentioned systems are recommended as an actual control process.

FIG. 13 is an example of such a combination system. This combination includes the program control system of FIG. 9, the interstand tension meter system of FIG. 10, and the rolling force meter system of FIG. 12. The main part of the combination system in FIG. I3 is the program control system having an alteration pattern concerned with roll peripheral speed. The alteration pattern of roll peripheral speed must be based on the following equation 5, besides the above-mentioned pattern concerned with equation I (FIG. 9).

Ah, is the alteration error of thickness based on other causes except a normal alteration command.

It is possible to easily detect Ah, by the system of FIG. 12 system based on formula 4. In this case, this formula 4 is rewritten as follows:

That is, if the alteration amount of AP, is off (-M-AS,) during a reducing alteration, the control pattern of equation I must be automatically switched to that of equation 5. During such control action, it is possible to detect whether or not the interstand tension is constant by the system of FIG. I0 directly and instantaneously. It is, however, not necessary to apply the equation 2 concerned with FIG. 10 as it is. While many factors in equation 2 have been already known because of equations l and 5, equation 2 cannot be rewritten with only unknown factors as follows:

i+| r fl+ nI' UiiI 6 The alteration pattern is comparatively simple. Accordingly, it is not necessary to be transmitted to the online computer 75. When minor loop devices having amplifiers 65, 66. 67, 68, 69, 70 and 7I are used, a fine alteration of the interstand tension is compensated with ease. And furthermore, the responsiveness of such minor loop devices is higher than that of the online computer system of FIG. 10.

Thus. the combination system as shown in FIG. 13 has excellent merits in that the faults of the basic control systems are eliminated and the advantages thereof are utilized. Such combination systems may be freely selected from the above four systems in consideration of mill conditions actually employed.

The gauge alteration processes of the present invention are effective to not only cold tandem mills. but also to reversing mills or to continuous hot-rolling mills.

While this invention has been explained with reference to detailed descriptions and drawings, it will be understood that the invention is not limited thereby and that many modifications can be made by those skilled in the art without departing from the inventive concepts set forth in the claims.

What we claim is:

1. In a multistand rolling apparatus for rolling a metal strip between pairs of rolls. a method of maintaining the interstand tension constant by predicting and automatically controlling the amount of gauge alteration at each stand during a rolling operation, comprising:

predetermining a basic pattern for altering roll peripheral speed at each stand corresponding to a fixed pattern of metal strip gauge alteration;

detecting a change in the roll opening;

computing values corresponding to a required amount of alteration of roll peripheral speed at a plurality of said stands as a function of said detected change in roll opening and as a function of said predetermined basic pattern; and

feeding forward said computed values to a plurality of said stands to control the roll peripheral speeds at said stands to thereby maintain the interstand tension constant.

2. A method as set forth in claim 1 wherein said change in roll opening is detected by a fixed program.

3. A method as set forth in claim 1 wherein said change in the roll opening is detected by measuring interstand tension with an interstand tension meter 4. A method as set forth in claim 1 wherein said change in roll opening is detected by measuring the thickness of the strip with a thickness meter at the delivery side ofa rolling stand.

5. A method as set forth in claim 1 wherein said change in roll opening is detected by measuring the rolling force at a stand with a rolling force meter.

6. A method as set forth in claim 1 wherein said change in roll opening is detected by the combination of a predetermined fixed program, measuring interstand tension. and measuring rolling force at a stand.

7. A method as set forth in claim 1 wherein said change in roll opening is detected by the combination of a predetermined fixed program, measuring interstand tension, and measuring the thickness of the strip at the delivery side ofa stand. 

1. In a multistand rolling apparatus for rolling a metal strip between pairs of rolls, a method of maintaining the interstand tension constant by predicting and automatically controlling the amount of gauge alteration at each stand during a rolling operation, comprising: predetermining a basic pattern for altering roll peripheral speed at each stand corresponding to a fixed pattern of metal strip gauge alteration; detecting a change in the roll opening; computing values corresponding to a required amount of alteration of roll peripheral speed at a plurality of said stands as a function of said detected change in roll opening and as a function of said predetermined basic pattern; and feeding forward said computed values to a plurality of said stands to control the roll peripheral speeds at said stands to thereby maintain the interstand tension constant.
 2. A method as set forth in claim 1 wherein said change in roll opening is detected by a fixed program.
 3. A method as set forth in claim 1 wherein said change in the roll opening is detected by measuring interstand tension with an interstand tension meter.
 4. A method as set forth in claim 1 wherein said change in roll opening is detected by measuring the thickness of the strip with a thickness meter at the delivery side of a rolling stand.
 5. A method as set forth in claim 1 wherein said change in roll opening is detected by measuring the rolling force at a stand with a rolling force meter.
 6. A method as set forth in claim 1 wherein said change in roll opening is detected by the combination of a predetermined fixed program, measuring interstand tension, and measuring rolling force at a stand.
 7. A method as set forth in claim 1 wherein said change in roll opening is detected by the combination of a predetermined fixed program, measuring interstand tension, and measuring the thickness of the strip at the delivery side of a stand. 